1. Field of the Invention
The present invention relates to a D/A converter.
2. Description of the Related Art
As an interface between digital signal processing and analog signal processing, a D/A converter (digital/analog converter) is employed. FIG. 1 is a circuit diagram which shows a configuration of a three-bit resistor string D/A converter. A D/A converter 100r includes a resistor string 10 including multiple resistors R connected in series and a switch circuit 12. Two reference voltages, i.e., a higher reference voltage VRH and a lower reference voltage VRL, are applied to respective terminals of the resistor string 10. According to a digital input code DIN(B2:B0), the switch circuit 12 selects one from among voltages that develop at respective connection nodes (taps) that each connect the adjacent resistors R.
The switch circuit 12 includes multiple two-to-one switches (selectors) SW connected to the multiple taps in tournament form. With such a D/A converter 100r, with the number of bits of the input digital code DIN as N (N represents an integer), the number of resistors R and the number of switches SW are each represented by 2N−1. Accordingly, as the number of bits N of the D/A converter increases, the number of resistors R and the number of switches SW increase in an exponential manner, leading to an increased circuit area.
In order to provide a reduced circuit area of such a resistor string D/A converter, several circuit configurations have been proposed (see Patent document 1, for example). However, even if such a technique described in Patent document 1 is employed, the circuit area increases in an exponential manner according to the number of bits N.
With an R-2R ladder D/A converter having a configuration other than a resistor string configuration, for example, such an arrangement provides a reduced circuit area. However, such an arrangement leads to a different problem of increased power consumption.